Triflic Acid‐Enabled Cascade Transformations of <i>o</i> ‐Quinone Acetates With 1,3‐Dicarbonyls

Brønsted acid catalysis unlocks an unconventional reactivity mode of electron‐deficient enols toward o ‐quinone acetates ( o ‐QAs). Herein, we report a general triflic acid‐enabled cascade transformation comprising regioselective 1,4‐addition, spontaneous demethylation, and condition‐dependent lactonization, which contrasts sharply with the well‐established 1,6‐addition behavior of 1,3‐dicarbonyl compounds under basic conditions. A systematic evaluation of β ‐keto esters, β ‐keto amides, 1,3‐diketones, and α , γ ‐diketo esters reveals that subtle electronic and stereochemical factors govern chemoselectivity, providing access to either meta ‐substituted phenols or 6,7‐disubstituted isocoumarins. Notably, α , γ ‐diketo esters undergo a highly α ‐selective cyclization, which density functional theory analysis attributes to a lower‐energy transition state arising from favorable carbonyl orientation and minimized CO‐π interactions. The resulting meta ‐phenolic adducts further enable late‐stage diversification and can be efficiently converted into isocoumarins or other heterocycles, demonstrating broad synthetic utility. Overall, this study reveals previously unexplored reactivity patterns of electron‐poor enols with o ‐QAs and establishes a versatile platform for accessing oxygen‐rich scaffolds relevant to natural product synthesis and medicinal chemistry.